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Dmitri Mendeleev
“The elements, if arranged according to their atomic weights, exhibit an apparent periodicity of properties.”
I. History
• A. Dimitri Mendeleev, 1869
• B. Moseley, 1914 – periodic law: The chemical and physical
properties of the elements are periodic functions of their atomic numbers; When the elements are arranged in order of increasing atomic number, there is a periodic repetition of their properties.
II. Structure/Organization• A. Periodic table
– Periods
– Groups or familiesValence electrons
• C. Nonmetals- Halogens- Noble gases
• B. Metals - Alkali metals
- Alkaline earth metals - Transition metals - Inner transition metals
- Representative elements
• D. Semimetals/metalloids
Ionization Potential/EnergyIE: Energy required to remove e-
Higher the IE: more difficult to remove e-
Across PeriodIE INCREASES* as the number of protons increases
* with decrease @ each subshellWhy? (effective nuclear charge)
Down GroupIE DECREASES as the number of shells
increasesWhy? (shielding, effective nuclear charge)
Electronegativity
The ability to attract e-
Across PeriodEN INCREASESBecause nuclear charge (# p+) increases
Down GroupEN DECREASESBecause more shells (n), more shielding, e- further away from nucleus
Atomic Radius
Across PeriodAtomic size DECREASES!Because nuclear charge (# p+) increases, as e- are added to same shell (n), pulls e- in tighter
Down GroupAtomic size INCREASESBecause more n (shells), more shielding,
e- further away from nucleus
Ionic Radius
IonCharged atom
CationPositive (+) ion (neutral atom looses e-)
AnionNegative (-) ion (neutral atom gains e-)
IsoelectronicSame electron structure
Ionic Radius
Across Period
IR DECREASES* (why?)
* with jump up in size @ metalloids!
Down Group
IR INCREASES
Compare to neutral atom
Valence e- are the outermost e- of an atom
D. Metallic character/nonmetallic character
Metallic CharacterIncreases
Nonmetallic character increases
Metallic Properties
Across Period
Metallic Properties DECREASES
Down Group
Metallic Properties INCREASES
Summary of Periodic Table Trends
• Moving Left --> Right • Atomic Radius Decreases • Ionization Energy Increases • Electronegativity Increases• Metallic character decreases • Moving Top --> Bottom • Atomic Radius Increases • Ionization Energy Decreases • Electronegativity Decreases • Metallic character increases